Propofol ensures a more stable A-line ARX index than thiopental during intubation

Background: The A-line autoregressive modelling with exogenous input index (AAI) is a new method of assessing depth of anesthesia. We examined the effects of tracheal intubation on the AAI and hemodynamics during induction of anesthesia with propofol compared with thiopental in patients aged over 50 yr. Methods: 40 patients scheduled for a laminectomy, posterior spinal fusion, vertebroplasty, or total hip replacement, ASA physical status I or II and aged over 50 yr, were randomly divided into two groups. Thiopental 5 mg·kg^-1 iv, fentanyl 2.5 μg·kg^-1 iv, and rocuronium 0.7 mg·kg^-1 iv were used in the thiopental group (n = 20) for anesthetic induction; the same protocol was used in the propofol group (n = 20) except that 2 mg·kg^-1 propofol iv was given instead of thiopental. The AAI, non-invasive blood pressure, and heart rate were measured every minute before induction for three minutes, at 1.5 mm post-induction, and then each minute post-intubation for eight minutes. Results: The AAI increased significantly at one and two minutes after intubation in the thiopental group (to 56.5 ± 18.6 at 1 min and 44.7 ± 18.7 at 2 min after intubation vs 19.9 ± 7.5 at 1.5 min after induction; P < 0.05). Thereafter, AAI values gradually decreased three minutes after intubation. The AAI was inhibited continuously after intubation in the propofol group, and no significant elevation was seen. Conclusion: Our results, using the AAI to monitor anesthetic depth during induction and tracheal intubation, suggest that at equipotent doses propofol provided a more stable level of anesthesia than did thiopental.